1. Field of the Invention
This invention relates to a printed circuit boards and, more specifically, to edge connectors disposed at the periphery of printed circuit boards.
2. Description of the Related Art
Printed circuit boards of the type used in various computer hardware, e.g., modems, commonly include a copper conductor over which is applied a layer of nickel metal followed by a layer of gold. Because of the complexity of applying a layer of gold over a layer of nickel on a copper conductor, and the associated relatively high cost of gold, there exists a need for a replacement for the gold and nickel materials in edge connectors on printed circuit boards.
The blending of resins or adhesives with powdered conductive materials such as, gold, silver, copper, nickel or other metals or alloys, provides conductive pastes or inks. Such materials, also known as polymer thick films (ptf), generally fall into two classes. One class is the thermosetting kind (preferred for permanence) of which the epoxys, acrylics, and polyesters are examples. The other class is the thermoplastic kind (which soften when heated) composed of synthetic or natural polymer, (such as, polyimide siloxane, nylon, neoprene, or rubber) in a solvent or other suitable carrier.
For further information pertaining to conductive inks, conductive adhesive inks, adhesives and surface mount technology, in general, the reader is directed to Radio-Electronics, page 59 et seq., November, 1987, "Introduction to SMT", by Forrest M.
Conductive inks typically include metals such as silver, copper, lead or tin to provide electrical conductivity together with polymeric binders which provide adhesion.
Conductive inks have been applied by screen printing onto non-moldable insulating baseboard substances, such as FR4 or glass epoxy.
However, when printed circuit boards are manufactured by applying a conductive paste such as copper paste on the insulating base board by screen printing, there is generally inadequate adhesion of the conductive paste or ink to the circuit terminal portion. This is particularly pervasive when heat is applied to the board during the soldering of electrical components to the terminal portion.
Also, specific levels of resistivity are required for use as edge connectors in Peripheral Component Interconnect (PCI), Industry Standard Architecture (ISA), and Audio Modem Riser (AMR) buses.